1. Field of the Invention
The present invention relates to a motorcycle with an exhaust gas sensor.
2. Description of Related Art
In recent years, increasingly stricter exhaust gas restrictions have been imposed on vehicles worldwide. To cope with such restrictions, vehicles use catalysts to purify exhaust gas in the exhaust pipe. In addition, vehicles must be equipped with an exhaust gas sensor for detecting the concentration of oxygen and the concentration of unburned gas in the exhaust pipe, thereby checking the actual air-fuel ratio of the engine to control the supply of fuel.
A structure for arranging or attaching an exhaust gas sensor for a motorcycle has been proposed. In the proposed structure, an exhaust gas sensor is arranged in a cylinder head of an internal combustion engine. In the cylinder head, an intake valve and an exhaust valve are arranged in a V-configuration at the top of the internal combustion engine. An exhaust port extends to curve from an axial direction of the exhaust valve in a direction opposite to the intake valve which intersects an axis of a cylinder. A downstream end of the exhaust port has a flange to which a member of an exhaust system is attached.
With this structure, the exhaust gas sensor is positioned around the flange of the exhaust port to be inclined relative to the axis of the cylinder, being located at the outside of the exhaust port. Accordingly, no large space is needed for the arrangement of the exhaust gas sensor, and no additional protector for the exhaust gas sensor is needed (see JP-A-2004-316430, Abstract and FIG. 4, for example).
Another structure for arranging an exhaust gas sensor for a motorcycle has been proposed. In a motorcycle including this structure, an engine with a bottom projection, such as an oil pan, is positioned between a front wheel and a rear wheel. An exhaust pipe extends from the engine rearward through the bottom side of the bottom projection. An exhaust gas sensor is attached vertically to a sensor attachment part on the upper part of the exhaust pipe and at a position separated rearward by a certain distance from the rear of the bottom projection.
With this structure, the exhaust gas sensor can be protected by the bottom projection and the exhaust pipe against flying stones. Thus, the need for a protective cover can be obviated, effecting a reduction in cost of design and production (see JP-A-Hei 11-343895, Abstract and FIG. 2, for example).
JP-A-2004-316430 is directed to the structure of arranging an exhaust gas sensor for a scooter-type motorcycle. JP-A-Hei 11-343895 is directed to the structure for arranging an exhaust gas sensor for a large motorcycle having an oil pan at the bottom of an engine.
The scooter-type motorcycle described in JP-A-2004-316430 has a large cover covering the engine and parts around the engine and connected to a rider's seat. Thus, if the motorcycle only has the structure for preventing the exhaust gas sensor against stones flying from below, no additional protection against flying stones is needed for the exhaust gas sensor.
In the large motorcycle described in JP-A-Hei 11-343895, the exhaust gas sensor can be protected against flying stones by the bottom projection and the exhaust pipe. However, it is unsatisfactory that no consideration is given to foreign matter coming from the lateral sides.
Generally, most large motorcycles manufactured by Japanese motorcycle manufacturers are models shipped to Europe that are compatible with European exhaust gas restrictions stricter than Japanese exhaust gas restrictions.
Meanwhile, many motorcycles available in the Japanese market are small. Among others, on and off-road motorcycles (designed for running on both paved public roads and unpaved roads or roadless ground) have gained increasing popularity lately.
On and off-road motorcycles must typically have a lightweight structure. For this reason, covers and other similar parts are made as small as possible or omitted other than the minimum required. When an exhaust gas sensor is attached to an exhaust pipe of an on and off-road motorcycle, attachment of a protective cover causes problems related to weight which contradicts the requirements above.
In addition, an on and off-road motorcycle may often fall. Thus, protective measures must be taken against damage to various parts of the motorcycle in case of a fall.
Exhaust-gas sensors, especially O2 sensors, generally use oxygen extracted from the atmosphere to detect exhaust gas components in the exhaust pipe (detect the air-fuel ratio). Thus, if an ambient air inlet of the exhaust gas sensor is covered with foreign matter such as mud, ambient air will not be introduced smoothly, and the detection function of the sensor will be significantly damaged.
On and off-road motorcycles may run on bad roads having conditions such as slush, as well as in cities. Thus, the exhaust gas sensor must be protected against sprayed mud as well as flying stones.
More specifically, in commonly available motorcycles, the protection against flying stones only aims at preventing breakage of the exhaust gas sensor. The protection against sprayed mud aims at preventing the detection function of the sensor from being reduced.
However, the idea of protecting the exhaust gas sensor against sprayed mud as described above is not disclosed in JP-A-2004-316430 or in JP-A-Hei 11-343895. In addition, on and off-road motorcycles often undergo model changeovers. Installation of exhaust gas sensors will be indispensable for future new models of one and off motorcycles.